Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known foil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
During operation of a wind turbine, the rotation of the rotor blades through air generates aerodynamic noise. Due to the amplitude modulation (i.e., the peak-to-peak variation) of the aerodynamic noise, a “swooshing” or periodic pulsing sound is typically heard in the near field of the wind turbine (i.e., the area directly around the wind turbine). Such sounds are typically seen as a nuisance and, thus, regulations are typically put in place establishing maximum decibel (dB) levels for wind turbines operating around residential communities and other populated areas. As a result, wind turbines are typically designed to operate below these maximum dB levels. However, current research now suggests that the peak-to-peak amplitude of the modulated noise generated by wind turbines may be higher at locations in the far field ((i.e., locations a certain distance (e.g., 1-4 kilometers) away from the wind turbines) than in the near field due to propagation effects and/or constructive interference. As such, there is a risk that wind turbines operating below the maximum dB levels in the near field may actually be exceeding these levels in the far field.
Various methods have been proposed for reducing the noise emissions of wind turbines. For example, it has been proposed to reduce aerodynamic noise by de-rating all of the wind turbines within a wind turbine farm in order to keep turbine speeds low during time intervals (e.g., during nighttime or other times at which reduced noise is desired). However, such de-rating of the wind turbines significantly reduces the power production of the farm. Another proposed method is to actively pitch the blades of a wind turbine as the blades pass through a particular range of azimuth positions (e.g., pitching the blades as they pass from the one o'clock to the four o'clock position). However, similar to de-rating the wind turbines, such continuous feathering of the blades results in a significant reduction in overall power production.
Accordingly, a system and method for controlling the amplitude modulation of noise generated by a wind turbine that does not significantly reduce power production would be welcomed in the technology.